1. Field of the Invention
The present invention relates to an apparatus automatically preparing crystals of a biopolymer such as proteins and nucleic acids in accordance with a predetermined procedure.
2. Description of the Related Art
The atomic level structure determination of proteins by X-ray analysis has been made in molecular biology, protein engineering, etc., and solving the crystal structure of a portion helps in understanding the relationship between the three-dimensional molecular structure or atomic arrangement of the main chain of the amino acid and the enzyme action thereof.
In a crystal structure analysis of a protein, (1) it is necessary to determine the optimum conditions for preparing crystals of the protein with a very small amount of protein sample, and (2) a certain size (about several hundred micrometers) of a crystal is necessary for X-ray diffraction. Many factors have an influence on the crystallization of a protein, including the concentration of a protein, the kind and concentration of a neutral salt and an organic solvent, pH, temperature, and contaminants, etc. To obtain large and satisfactory crystals, the crystallization of a protein under zero gravity in space has been considered and tried.
Heretofore, the preparation of biopolymer crystals has been done manually by skilled persons in accordance with their skill and experience. But considerable time and work are necessary to determine the optimum conditions for crystal preparation, since there are many factors such as the concentration of a biopolymer, the kind and concentration of a biopolymer insolubilizing agent, the ionic strength, pH, and temperature of a reaction solution, etc. Further, in manual operation, the results may be varied by slight differences in procedure, resulting in an undesirable low reproducibility.
K. Nakamura and Y. Mitsui in "Crystallization of Protein by Hanging-drop Method" Rigaku Denki Journal 16, 1985, pp 12-14 describe a hanging-drop method in which a vessel for tissue culture having a plurality of reservoirs is used so that the crystallization conditions of a protein are examined systematically.
In this operation, a sample solution and ammonium sulfate solution are dropped on a coverglass by means of a digital micropipette and combined by means of a fine glass rod. The coverglass is then placed upside down on a reservoir, and this operation is repeated for all reservoirs. This operation is disadvantageous in that, if the operation is not done quickly, water evaporation changes the concentration of the solution.
Other known apparatuses for preparing biopolymer crystals include that disclosed by, for example, Walter Littke and Christina John in "Protein Single Crystal Growth Under Microgravity", SCIENCE, Vol. 225, pp 203-204; and Yuhei Moriguchi in "Crystal Growth of Proteins under Microgravity", "Nihon Kessho Gakkai Shi (Japanese Journal of Crystallography)" 28, 47 (1986) pp 47-49. All of these apparatuses were developed for use in space, but were not intended to provide an automated apparatus. Further, an apparatus for preparing biopolymer crystals in a land-based laboratory has not been proposed.